1. Field of the Invention
The present invention relates to a rod-shaped light guide operative to receive light at an end face and emit light at a predetermined emitting portion, and to an image reading device having a rod-shaped light guide built therein.
2. Description of the Related Art
Facsimile machines, copiers, and scanners have a built-in image reading device provided with a rod-shaped light guide for illuminating a document with a line light and with a lens array for condensing light reflected from the document onto a line image sensor.
In such an image reading device, a document may be placed on a glass plate such that a portion of the document is elevated. In order to read from the elevated portion of the document (hereinafter, referred to as elevated portion), the elevated portion needs to be illuminated with sufficient brightness. Variation in light intensity occurring when the document is elevated is represented as depth of illumination. Patent document No. 1 discloses a technology whereby a deflecting means, for bringing the optimum light intensity distribution close to the optical axis of the lens array by shifting light intensity distribution of the emitted light in the sub-scanning direction, is provided in a light emitting portion of a rod-shaped light guide in order to achieve sufficient light intensity and obtain proper depth of illumination. [patent document No. 1] JP 2006-148501
However, while the technology disclosed in patent document 1 is capable of increasing light intensity at a desired position, there is still room for improvement in depth of illumination.